Cultural paper which has been a medium for the delivery of information and advertisement, gradually hands over its position to the digital media as popularization of computer and commercialization of internet are realized and innovative development of other electric communication apparatus advance. The method of publishing books and magazines changes from ‘printing and distribution’ into ‘distribution and printing,’ and big demand for an adequate paper is expected with the growth of digital system. Unlike the conventional system (printed and bound books are sold in bookstores), the recent digital system sends the information through internet and then a dealer or a consumer searches the information and if wanted the dealer or the consumer prints the information directly by formatted digital printing method. And this digital printing system is expected to be generalized in near future.
The digital printing can be divided largely into two different methods; toner type and ink-jet type. In the late 2000, the digital printing already held 41% of the market in the case that required copies were up to 2000. And its market sharing will be soon as high as the conventional offset printing.
The ink-jet type, the most universal type for digital printing, has been generally used for multiple color printing, which will extend its market sharing according to the generalization of digital camera and the use of images on internet. Up to date, silica has been used as a major material and polyvinyl alcohol and polyvinyl acetate have been used as a binder for the production of ink-jet paper. To increase preservation and image reproducibility, more upgraded materials are multi-layered for photopapers.
The reason of using polyvinyl alcohol and polyvinyl acetate as a binder is that the major material silica has a very wide specific surface area asking a high adhesive force and they have excellent compatibility with ink-jet ink comprising soluble dye. In addition, polyvinyl acetate has a weak ionic strength, suggesting that it does not interact with polydiallyldimethylammonium chloride (polyDADMAC) which is a cation additive used for the production of a coating liquid for ink-jet paper, so that quantum properties for ink-jet paper can be well preserved. However, these water-soluble binders, polyvinyl alcohol and polyvinyl acetate, are very expensive materials and intensively increase the viscosity of a coating liquid, resulting in the decrease of coating workability, the increase of energy cost for drying process and deterioration of the quality of ink-jet paper. In particular, it has been pointed that polyvinyl acetate causes irregularity of a product and has insufficient functions as an ink-jet binder.